@revk @penguin42 @andrew @neil No the postal service is special here
You have an interest in proving and email was or was not delivered. You can tamper with or lose your server logs. Stuff can get lost. SMTP is not reliable
The post office is notionally an uninterested third party with a process in place to manage high reliability document delivery and recognized as such.
The analogy would be not using email but both using an agreed reliable third party provider of electronic document service